Heat-stable greases and method of preparation



3,002,926 HEAT-STABLE GREASES AND METHOD F PREPARATION 1 Charles R. Bergen, Monroeville, Pa., assignor to'Continental Oil Company, Ponca City, Okla, acorporation of Delaware No Drawing. Filed July 3, 1958, Ser. No. 746,336 13 Claims. (Cl. 252-35) This invention relates to improved grease compositions and more particularly to the production of heat-stable grease compositions utilizing as one of the components a gelling agent formed by reacting a polycarboxylic acid with a metal salt.

For many years commercial greases have been produced predominantly by using as one of the components normal soap-forming ingredients, such as'the metal salts of an acid derived from animal and vegetable fats. Although such greases are satisfactory for many purposes, they are unsuitable at temperatures attained by many modern machines during the normal operation of such machines. When such greases are subjected to relatively high temperatures, the soap tends to dissolve or at least form a colloidal dispersion in the lubricating oil base with consequent loss of the mechanical structure which characterizes a grease-like composition; furthermore, these greases, asa general rule, donot reform spontaneously upon cooling. As a result, such greases are unsuitable for use in the lubrication of bearings which attain such elevated temperature. I

Several methods of preparing heat-stable greases have been proposed in. the prior art. One proposal incorporates certain salts of aromatic acids, such as sodium benzoate, in the grease composition. Apparently material forms complexes with the normal'soap-form ing acids. While these-additives impart heat stability to the resulting grease, it is necessary to heat such grease compositions during the process of manufacture to a temperature of at least 500 to 600 F. This is a disadvantage because temperatures in this range involve fire hazards and promote oxidative degradation of the hired States Patent O vention to provide an improved grease which obviates oil carrier. Anothermethod proposed for the preparathedisadvantages of the prior art grease compositions. It is another object of our invention to produce a grease which is stablea't elevated temperatures. It is still another object of this invention to produce a grease having an improved fibrous structure, superior mechanical characteristics, and having high water resistance. O-therv objects and advantages of the invention will become apparent as the invention is hereinafter more thoroughly described.

In accordance with the present invention, greases of the above-described characteristic are obtained by first forming a gelling agent by reacting a metal salt with a low molecular weight polycarboxylic acid in a mutual solvent, wherein the cation of said metal salt is select t ed from groups 2 and 3 of the periodic table and the anion is either a halide, alcoholate, or alcoholate-carbonate complex radical. Said gelling agent is preferably prepared in situ in an oleaginous liquid whereby a grease composition is produced following removal of the solvents. Alternatively, the gelling agent may be prepared in the absence of an oleaginous liquid and then later may be added to the oleaginous liquid with milling to produce a grease.

Before proceeding with a specific example illustrating my invention, it may be well to list the different components and the relative quantities of each used in the process. Suitable polycarboxylic acids which may be employed in the processinclude the following:

Generally, however, I prefer the dicarboxylic acids;

' and of these my preference is 3-methyl glutaric acid.

nous liquid vehicle; U.S. Patent No. 2,625,508 to Fred H. Stross. describes this procedure. Whichever procedure is used, several disadvantages are inherent in the process, as, for example, a hydrogel is bulky and difficult to handle; the gel must be washed to remove salts; and hydrogels contain a large amount of waterwhich must be removed. a

The useof low molecular weight monocarboxylic acids in greases is well known. The principal disadvantage involved in the use of monocarboxylic acids is that the resulting greases are 'soft and lacking in fibrous structure. a

Previousmethods of preparing a gelling agent comprising metal salts of polycarboxylic acids have involved the use of dispersing agents. Accordingly, the final It is, therefore, a principal object'of the present in- Suitable oleaginous liquid vehicles employed in these compositions may be mineral lubricating oils obtained by any of the conventional refining processes; vegetable oils, such as corn oil, cottonseed oil, etc.; animal oils, such as lard oil, sperm oil, etc.; and various synthetic lubricants, such as the polyalkylene glycols, various high molecular weight esters, silicone polymer oil, etc.

Suitable solvents useful in the process of my invention include aromatic hydrocarbons, ketones and the low molecular weight aliphatic alcohols. In some cases it may be desirable to employ a solution of two or more of these solvents. The selection of particular solvent or combinations of solvent is dependent upon the reactants used.

Suitable metal salts are those in which the cation is selected from group 2 or 3 of the periodic table, and the anion is either a halide, alcoholate, carbonate, or an alcoholate-oarbonate complex. Preferred cations include aluminum, barium, and magnesium.

Preparation of alcoholates of polyvalent metals are described in U.S. Patent No. 2,594,822 (Stross et al., 'April 29, 1952). Preferably, a carbon dioxide-metal alcoholate complex is employed. Such a complex, which may be formed by passing carbon dioxide through themetal Component Suitable Preferred Range Range Poiycarboxyllc acid 1 l M al salt 0.4-1.8 64.4 Oleaginous vehicle- 3 5-1.5.0 4 911. 5 Solvent- 25-100 32 78.4

The actual temperature employed during the process of preparing these greases may vary over a rather wide range. A suitable temperature range may vary from about 16 C. to about 150 C. For most purposes, I prefer to operate at a somewhat lower temperature than the maximum given above, and under such conditions I prefer to operate within a temperature range which varies from about 16 C. to 105 C.

As to the time of reaction, I have found that the reaction will be complete upon thorough mixing of the components followed by removal of the solvents.

While I do not wish to be bound by any particular theory as to the mechanism of the formation of the gelling agent, I believe that the correct explanation is substantially as follows. This explanation will be @given wherein the metal used is divalent, specifically magnesium. The magnesium salt and the polycarboxylic acid react to form a polymeric material which is exemplified by the following formula:

0 -0M 0-ii-(0Hr)nii-O-M -O- wherein n is an integer varying from 1 to 4.

In order to disclose the nature of the present invention more clearly, the following examples will be given. It is to be understood, however, that the invention is not to be limited to the specific conditions and details set forth in these examples except insofar as such limitations are specified in the appended claims. In the examples, the numerical value preceding pale oil designates the viscosity at 100 F. in Saybolt second Universal units. Dropping points of the products were determined by ASTM test D-566-42. Water washout data were obtained by following the procedure as given in ASTM test D-1264-53T. Parts given are parts by weight.

EXAMPLE I To a vigorously stirred grease kettle were charged:

77.5 parts 170 pale oil 263.7 parts benzene To this were added simultaneously and rather slowly the following two solutions:

Solution 1 10.65 parts aluminum isopropoxide dissolved in 175.8 parts benzene.

Solution 2 7.84 parts S-methyl glutaric acid dissolved in 175 .8 parts benzene.

The solvent was removed by distillation under vacuum to 85 C. The product was then passed twice through a homogenizer set to release at 5,000 p.s.i.

The product had a worked penetration of 4 l EXAMPLE II A C0Mg(OCH;,)- complex was first prepared by the following technique: A vessel equipped with a reflux condenser and a fritted glass tube for entry of gas was charged with 180 parts of anhydrous methanol and 10 parts of magnesium turnings. The reaction proceeded at reflux temperature, and after a period of 8 hours, evolution of hydrogen had ceased and the mixture consisted of a suspension of finely divided insoluble material in alcohol. Into this suspension was passed carbon dioxide until the mixture was acid to alpha napthol benzein. At this point 35.2 pants of carbon dioxide had been absorbed. The resulting clear methanol solution analyzed 4.5 percent magnesium.

The following materials were then charged to a pot while agitation was maintained:

84.4 parts 400 pale oil 176 parts benzene 79 parts acetone 47 parts of the methanolic solution of the Co -complex While maintaining agitation, a solution containing the following was gradually added:

13 parts 3-methyl glutaric acid 88 parts benzene 79 parts acetone The solvents were removed by heating to C. After homogenizing, the product was a straw-colored grease having a dropping point of above 450 F. A washout loss of 3.9 percent was obtained on this material.

EXAMPLE III Example 11 was repeated with the exception that 80.0 parts of a methanolic solution of BaO having a Ba content of 15.3 percent was substituted for the magnesium containing solution. 0n removing the solvents and homogenizing, a grease was obtained having a dropping point above 450 F. This material had a washout loss of 3.8 percent.

EXAMPLE IV The following materials were charged to a pot while stirring:

17 0 parts 400 pale oil 700 parts benzene A second solution was prepared containing the followmg:

554 parts acetone 78 parts tertiary butyl alcohol 178 parts methanol 26.45 parts isophthalic acid 8017 parts of a methanolic solution of a complex of Mg(-OCH and CO having an Mg content of 4.6 percent The second solution was added to the pot, and the total mixture was thoroughly agitated.

The solvents were removed by heating to 105 C., after Which the product was homogenized. The resulting grease had a dropping point of above 450 F. It was water resistant, having a washout loss of 4.5 percent.

EXAMPLE V A grease containing aluminum diglycollate was pre pared in the following manner: 10.9 parts of aluminum isopropylate were dissolved in 88 parts of boiling benzene (solution A). 8.13 parts of diglycollic acid were dissolved in 80 parts of isopropanol (solution B). 90 parts of 400 pale oil were dissolved in 230 parts of benzene (solution C). Solutions A and B were added slowly to solution C. The solvents were removed by heating to 78 C. under a moderate vacuum, after which the material was homogenized.

This product had a worked penetration of 370 mm. X 10- Its dropping point was above 450 F. The washout loss was 5.2 percent.

EXAMPLE VI A concentrated aqueous solution of AlCl -6H O was poured into a solution of the sodium salt of 3-methy1 glutaric acid. The acid was present in slight excess over the theoretical amount necessary to form A1(OH) 3-methy1 glutarate. The product was filtered and washed with water. It was then dried in a vacuum desiccator. 25 parts of this product were worked into 75 parts of di-Z-ethyl hexyl azelate. A grease resulted having a penetration of 320 mm. l" The dropping point was above 450 F. It was resistant to emulsification and had a water washout loss of 5.8 percent.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto, since many modifications may be made; and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. The method of preparing a lubricating grease composition which comprises the steps of forming a gelling agent in situ by reacting about .4 to 1.8 parts of a metal salt with about 1 part of a polycarboxylic acid selected from the group consisting of itaconic acid, Z-methyl adipic acid, 3-tertiary butyl adipic acid, S-tertiary amyl adipic acid, mercapto succinic acid, 2,3-dibromo succinic acid, 5-methyl-4-cyclohexene-1,2-dicarboxylic acid, benzylmalonic acid, terephthalic acid, thiodiglycolic acid, pyromellitic acid, isophthalic acid, diglycollic acid, and 3-methy1 glutaric acid, said reactants being in solution in about 25 to 100 parts of a mutual solvent, in the presence of about 3.5 to 15 parts of an oleaginous liquid, wherein the cation of said metallic salt is selected from the group consisting of the metals of groups 2 and 3 of the periodic table and the anion is selected from the group consisting of halide, alcoholate, carbonate, and alcoholatecarbonate complex radicals, removing the solvents by heating to a temperature of not greater than about 150 C., and then homogenizing the reaction mixture.

2. The method of claim 1 wherein the cation of the metallic salt is aluminum.

3. The method of claim 1 wherein the cation of the metallic salt is magnesium.

4. The method of claim 1 wherein the polycarboxylic acid is 3-methyl glutaric acid.

5. The method of claim 1 wherein the metallic salt is aluminum isopropoxide.

6. The method of claim 1 wherein the metallic salt is a magnesium methylate-carbon dioxide complex.

7. The method of claim 1 wherein the oleaginous liquid is a mineral lubricating oil.

'8. A lubricating grease composition prepared in accordance with the method of claim 1.

9. The method of claim 7 wherein (1) the metal salt is aluminum isopropoxide and (2) the polycarboxylic acid is 3-methyl glutaric acid.

10. The method of claim 7 wherein (1) the metal salt is a magnesium methylate-carbon dioxide complex and (2) the polycarboxylic acid is 3-methyl glutaric acid.

11. The method of preparing a lubricating grease composition which comprises the steps of forming a gelling agent in situ by reacting about 6 to 1.4 parts of a metal salt with about 1 part of a polycarboxylic acid selected from the group consisting of itaconic acid, -2-methyl adipic acid, 3-tertiary butyl adipic acid, 3-tertiary amyl adipic acid, mercapto succinic acid, 2,3-dibromo succinic acid, 5-methyl-4-cyclohexene-1,Z-dicanboxylic acid, benzylmalonic acid, terephthalic acid, thiodiglycolic acid, pyromellitic acid, isophthalic acid, diglycollic acid, and S-methyl glutaric acid, said reactants being in solution in about 32.5 to 78.4 parts of a mutual solvent, in the presence of about 4.9 to 11.5 parts of an oleaginous liquid, wherein the cation of said metallic salt is selected from the group consisting of the metals of groups 2 and 3 of the periodic table and the anion is selected from the group consisting of halide, alcoholate, carbonate, and alcoholate-carbonate complex radicals, removing the solvents by heating to a temperature of not greater than about C., and then homogenizing the reaction mixture.

12. The method of claim 11 wherein (1) the metal salt is aluminum isopropoxide, (2) the polycarboxylic acid is 3-methyl glutaric acid, and (3) the oleaginous liquid is a mineral lubricating oil.

13. The method of claim 11 wherein (1) the metal salt is a magnesium methylate-carbon dioxide complex, (2) the polycarboxylic acid is 3-methyl glutaric acid, and (3) the oleaginous liquid is a mineral lubricating oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,349,817 Farrington et al. May 30, 1944 2,363,514 Farrington et al Nov. 28, 1944 2,469,041 Jones May 3, 1949 2,528,373 Knowles et a1 Oct. 31, 1950 

1. THE METHOD OF PREPARING A LUBRICATING GREASE COMPOSITION WHICH COMPRISES THE STEPS OF FORMING A GELLING AGENT IN SITU BY REACTING ABOUT .4 TO 1.8 PARTS OF A METAL SALT WITH ABOUT 1 PART OF A POLYCARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF ITACONIC ACID, 2-METHYL ADIPIC ACID, 3-TERTIARY BUTYL ADIPIC ACID, 3-TERTIARY AMYL ADIPIC ACID, MERCAPTO SUCCINIC ACID, 2,3-DIBROMO SUCCINIC ACID, 5-METHYL-4-CYCLOHEXENE-1,2-DICARBOXYLIC ACID, BENZYLMALONIC ACID, TEREPHTHALIC ACID, THIODIGLYCOLIC ACID, PYROMELLITIC ACID, ISOPHTHALIC ACID, DIGLYCOLLIC ACID, AND 3-METHYL GLUTARIC ACID, SAID REACTANTS BEING IN SOLUTION IN ABOUT 25 TO 100 PARTS OF A MUTUAL SOLVENT, IN THE PRESENCE OF ABOUT 3.5 TO 15 PARTS OF AN OLEAGINOUS LIQUID, WHEREIN THE CATION OF SAID METALLIC SALT IS SELECTED FROM THE GROUP CONSISTING OF THE METALS OF GROUPS 2 AND 3 OF THE PERIODIC TABLE AND THE ANION IS SELECTED FROM THE GROUP CONSISTING OF HALIDE, ALCOHOLATE, CARBONATE, AND ALCOHOLATECARBONATE COMPLEX RADICALS, REMOVING THE SOLVENTS BY HEATING TO A TEMPERATURE OF NOT GREATER THAN ABOUT 150* C., AND THEN HOMOGENIZING THE REACTION MIXTURE. 